1. Field of the Invention
This invention relates to fall board stoppers for keyboard instruments such as grand pianos.
2. Description of the Related Art
Keyboard instruments (e.g., grand pianos in particular) have fall boards whose opening angles are approximately set to 90°, and when fall boards are closed, they are held roughly in parallel with keybeds for arranging keys, while when maximally opened, fall boards are held roughly perpendicular to keybeds.
An example of a conventionally-known grand piano equipped with a fall board will be described with reference to FIGS. 7A and 7B, wherein FIG. 7A is a cross sectional view showing essential parts interlocked with the fall board of the grand piano, and FIG. 7B is a side view specifically showing the fall board and its related parts. Herein, reference numeral 1 designates a fall board, 2 designates a keybed, 3 designates a key slip, 4 designates an upper beam, 5 designates a lock slip, 6 designates a top board, 7 designates a pin block, and 8 designates a side board, all of which are assembled together to form a casing 10, which also incorporates a keyboard 11, actions, strings, and the like.
The backend portion of the fall board 1 is pivotally supported by a pair of open/close devices 12 at right and left ends thereof, so that the fall board 1 can be freely rotated about a prescribed axis thereof, or it can be vertically opened or closed over the keybed 2. A bent portion 1a is formed at the tip end of the fall board 1, which is therefore supported by the upper surface of the key slip 3 when closed (see solid-line illustration in FIG. 7A), whereby the fall board 1 is roughly maintained in parallel with the keybed 2. When opened, the fall board 1 is stood against and in proximity to the exterior surface of the upper beam 4 (see dashed-line illustration in FIG. 7A), so that the fall board 1 is maintained roughly perpendicular to the keybed 2 and is slightly slanted backwards.
As shown in FIG. 7B, each of the open/close devices 12 that are attached to both ends of the backend portion of the fall board 1 is constituted by a shaft 15 and a metal member 16 having a roughly U-shaped bearing hollow 17, wherein the shaft 15 is loosely engaged with the hollow 17 and is supported by the metal member 16 in a free-rotation manner. That is, the backend portion of the fall board is equipped with a pair of shafts 15 that are slightly projected from both ends thereof and a pair of metal members 16 that are fixed to interior surfaces of the side boards 8, which are arranged on both sides of the keybed 2. Incidentally, the shafts 15 form a rotation center ‘O’ allowing the fall board 1 to be rotated thereabout.
A weight (or weights) 18 is attached to a prescribed position of the backend surface of the fall board 1 and is normally located above the rotation center O when the fall board 1 is closed (see FIG. 7A). Due to the provision of the weight 18, it is possible to improve stability in operating the fall board 1, which is therefore prevented from being normally (or unexpectedly) closed due to vibration and the like. When the fall board 1 is opened, the weight 18 attached to the backend surface of the fall board 1 is moved downwards and is located backwardly from the rotation center O; that is, the weight 18 imparts a prescribed rotation behavior to the fall board 1 in a backward direction, which in turn prevents the fall board 1 from easily falling down in a forward direction (toward a player's side).
As the material for the weight 18, it is possible to use lead that may be inexpensive and that has a high specific gravity among metal materials used in industrial fields. However, the lead is a heavy metal that is harmful to the human body and the natural environment; therefore, it may be preferable not to use it in view of protection of the environment. For this reason, there are recently provided other types of fall board structures that prevent fall boards from unexpectedly falling down without the use of lead weights, examples of which are disclosed in Japanese Patent Application Publication No. Hei 9-62252 and Japanese (Examined) Utility Model Publication No. Hei 5-48238.
In a keyboard instrument disclosed in Japanese Patent Application Publication No. Hei 9-62252, a pair of magnets are respectively attached to the backend surface of a fall board and a corresponding portion of a keyboard, so that when the fall board is opened, the magnet attached to the backend surface of the fall board is moved close to the magnet attached to the keyboard, whereby due to magnetic force exerted between the magnets, the fall board is maintained in an opened state and is prevented from unexpectedly falling down due to vibration and the like.
In a keyboard instrument disclosed in Japanese Utility Model Publication No. Hei 5-48238, a rotary damper utilizing viscous resistance of fluid is used as an open/close device for a fall board. When the fall board is opened, the rotary damper is reduced in viscous resistance of fluid; therefore, it allows the fall board to be manually opened with force similar to that of a normal fall board not equipped with the rotary damper. When the fall board is closed, the viscous resistance of fluid of the rotary damper is gradually increased as the tip end of the fall board descends down to the keybed, so that the fall board is controlled in downward movement. This allows the user of the keyboard instrument to slowly move down and close the fall board.
Both of the conventionally-known fall board structures adapted to the aforementioned keyboard instruments may not provide a sufficient degree of stability in operation when fall boards are opened. That is, the fall board structure using the magnet as disclosed in Japanese Patent Application Publication No. Hei 9-62252 utilizes magnetic absorption in maintaining the fall board in position, which however cannot completely fix the fall board in an opened state; therefore, when an external force is accidentally applied to the fall board, the fall board may be rotatably moved and closed with ease.
The other fall board structure using the rotary damper as disclosed in Japanese Utility Model Publication No. Hei 5-48238 may be advantageous in that it can reliably prevents the fall board from rapidly falling down, wherein the controlling force applied to the fall board depends upon a load resistance that occurs as the fall board is rotated. Therefore, when an external force is applied to the fall board, which is opened, in a closing direction, it may be difficult to reliably stop the fall board from falling down.